Hi

Any real crystal you buy will have a tolerance on the angle. In the case of a crystal cut for turn
the temperature will be a bit different and you will match your oven to it. If you attempt a zero
angle cut, you will never really hit it and there is no way to compensate for the problem.

Bob

That is not true.  I say that thermal coolers have made ovens obsolete.  A
zero temperature coefficient at room temperature is easier to hit than a
zero temperature at the upper turnover point when such a thing exists.  See
curve 0 in Figure 6 at https://coloradocrystal.com/applications/ .

πθ°μΩω±√·Γ
WB0KVV

On Friday, June 2, 2017, Bob kb8tq <kb8tq@n1k.org
javascript:_e(%7B%7D,'cvml','kb8tq@n1k.org');> wrote:

You have a fundamental misunderstanding of the AT curve family.  See
my QBASIC plot at
http://gonascent.com/papers/hp/hp5061/photos/newxtl.jpg .  The
commonly described AT cut is shown as the largest sine wave in the
blue rectangle.  The left side of the rectangle is -55°C, the center
is 25° C and the right side is 105° C.  The bottom of the rectangle is
-16 ppm and the top is +16 ppm.

Main Cut
Temp  Freq
-55° C -16 ppm
-15° C +16 ppm
+25° C ±0 ppm
+65° C -16 ppm
105° C +16 ppm

You can get a lower turnover point of 24° C and an upper turnover
point of 26° C. Their amplitude would be °±0.250 ppb.  As the turnover
points approach each other, their amplitude approaches zero.  The line
joining all the turnover points is y= -8·x^3.  The zero temperature
for 25° is y=4·x^3.  Practical tolerance these days is on the order of
0.1 minutes of arc.  This is within the width of the traces in the
graph.

You are way off on your 0° to 50° C crystal.

["Umm …. errr … it’s quite easy to get a +/- 2 ppm 0-50C AT cut
including the tolerance on the cut angle."]

Temp  Freq
0° C  -0.488 ppb (lower limit)
12.5° C  +0.488 ppb (lower turning point)
25° C  ±0
37.5° C  -0.488 ppb (upper turning point)
50° C +0.488 ppb (upper limit)

As I claimed, a Thermal Electric Cooler has never been used to build a
crystal oscillator.  In the 50s, TEC efficiencies were on the order of
1% and were useless.  The Soviets made coolers more practical in the
70s with better materials.  I saw one used at Telemation that was able
to measure dew point by condensing water vapor on a mirror.  It looks
like efficiencies have now improved to 33% or so.

It was only in the early 70s that Analog Devices invented the AD590
solid state temperature sensor.  It made thermister bridges obsolete.
Switching amplifiers are required to drive thermal coolers if you want
to preserve efficiency.

πθ°μΩω±√·Γλ
WB0KVV

---------- Forwarded message ----------
From: Bob kb8tq kb8tq@n1k.org
Date: Fri, Jun 2, 2017 at 12:22 PM
Subject: Re: HP5061B Versus HP5071 Cesium Line Frequencies
To: "Donald E. Pauly" trojancowboy@gmail.com
Cc: "rward0@aol.com" rward0@aol.com, time-nuts time-nuts@febo.com

Hi

Any real crystal you buy will have a tolerance on the angle. In the
case of a crystal cut for turn the temperature will be a bit different
and you will match your oven to it. If you attempt a zero angle cut,
you will never really hit it and there is no way to compensate for the
problem.

Bob

On Jun 2, 2017, at 3:19 PM, Donald E. Pauly trojancowboy@gmail.com wrote:

A cut at that angle has no turn over temperature. The zero temperature
coefficient point is 25°.  Its temperature coefficient everywhere else
is positive.

On Friday, June 2, 2017, Bob kb8tq kb8tq@n1k.org wrote:

On 6/3/17 9:56 PM, Donald E. Pauly wrote:

There is a difference between something like a platinum resistance
thermometer (PRT or RTD) and a thermistor, but they both are "measure
resistance to measure temperature" devices.

Yes, the AD590 is a useful part (I've got some in a device being
launched in August), but PRTs,thermistors, and thermocouples are still
widely used.

I don't know that the inherent precision (at room temperature)of the
various techniques is wildly different.  A 1mV/K signal (AD590 into a 1k
resistor) has to be measured to 0.1mV for 0.1 degree accuracy.  That's
out of 300mV, so 1 part in 3000

A type E thermocouple is 1.495 mV at 25C and 1.801 at 30C, so about 0.06
mV/K slope. Measure 0.006mV for 0.1 degree  (plus the "cold junction"
issue).  1 part in 250 measurement.

Modern RTDs all are 0.00385 ohm/ohm/degree at 25C.  Typically, you have
a 100 ohm device (although there are Pt1000s), so it's changing 0.385
ohm/degree.  1 part in 3000

Checking the Omega catalog.. A 44007 has nominal 5k at 25C, and is 4787
at 26C, so 1 part in 24.

Especially these days, with computers to deal with nonlinear calibration
curves, there's an awful lot of TCs and Thermistors in use. The big
advantage of the AD590 and PRT is that they are basically linear over a
convenient temperature range.

In a variety applications, other aspects of the measurement device are
important - ESD sensitivity, tolerance to wildly out of spec temperature
without damage, radiation effects etc.  Not an issue here, but I'll note
that the thermistor, PRT, and thermocouple are essentially ESD immune.
The AD590 most certainly is not.

If you go out and buy cheap industrial PID temperature controller it
will have input modes for various thermocouples and PRTs.  I suppose
there's probably some that take 1uA/K, but it's not something I would
expect.

So I wouldn't say thermistor bridges (or other temperature measurements)
are obsolete.

In message 3ca81847-63c4-f803-994d-8e07c9973ba0@earthlink.net, jimlux writes:

Depending how much money you want to spend, you can also get pt10k
and even pt100k RTD's, to satisfy particular needs for resolution,
self-heating, inductance, mass and the many and varied noises.

And if course, we cannot talk PT100 and fail to repeat the old pun:

"PT100 is the gold standard for temperature measurement"

:-)

--
Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
FreeBSD committer      | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

Hi

Have you ever tried to actually buy a crystal built to a specification? There is a
tolerance on them. That has a profound impact on what you can buy.

Bob

I stand by my remark that thermistors have been obsolete for over 40
years.  The only exception that I know of is cesium beam tubes that
must withstand a 350° C bakeout.  Thermistors are unstable and
manufactured with a witches brew straight out of MacBeth.  Their
output voltages are tiny and are they inconvenient to use at different
temperatures.

Where did you get the idea to use a 1 k load for an AD590?  If you run
it from a -5 V supply you can use a 15 k load to a +5V supply.  This
gives 15 V/C° output.  If you drive it from a 10 Meg impedance current
source, you get 30,000 V/ C°.  If I remember correctly, I drove a
power MOSFET heater gate directly in my prototype oven 20 years ago.
It would go from full off to full on in 1/15 ° C.  Noise is 1/25,000 °
C in a 1 cycle bandwidth.

The room temperature coefficient of an AT crystal is -100 ppb per
reference cut angle in minutes.  (-600 ppb/C° for standard crystal)
The practical limit in a crystal designed for room temperature is
about 0.1' cut accuracy or ±10 ppb/C°.  If you have access to an
atomic standard, you can use feed forward to get ±1 ppb/C°.  If the
temperature can be held to ±0.001° C, this is ±1 part per trillion.
This kind of accuracy has never been heard of.  Feed forward also
allows you to incorporate the components of the oscillator into the
thermal behavior.  It does no good to have a perfect crystal if the
oscillator components drift.

πθ°μΩω±√·Γλ
WB0KVV

---------- Forwarded message ----------
From: jimlux jimlux@earthlink.net
Date: Sun, Jun 4, 2017 at 4:47 AM
Subject: Re: [time-nuts] Fwd: HP5061B Versus HP5071 Cesium Line Frequencies
To: time-nuts@febo.com

On 6/3/17 9:56 PM, Donald E. Pauly wrote:

There is a difference between something like a platinum resistance
thermometer (PRT or RTD) and a thermistor, but they both are "measure
resistance to measure temperature" devices.

Yes, the AD590 is a useful part (I've got some in a device being
launched in August), but PRTs,thermistors, and thermocouples are still
widely used.

I don't know that the inherent precision (at room temperature)of the
various techniques is wildly different.  A 1mV/K signal (AD590 into a
1k resistor) has to be measured to 0.1mV for 0.1 degree accuracy.
That's out of 300mV, so 1 part in 3000

A type E thermocouple is 1.495 mV at 25C and 1.801 at 30C, so about
0.06 mV/K slope. Measure 0.006mV for 0.1 degree  (plus the "cold
junction" issue).  1 part in 250 measurement.

Modern RTDs all are 0.00385 ohm/ohm/degree at 25C.  Typically, you
have a 100 ohm device (although there are Pt1000s), so it's changing
0.385 ohm/degree.  1 part in 3000

Checking the Omega catalog.. A 44007 has nominal 5k at 25C, and is
4787 at 26C, so 1 part in 24.

Especially these days, with computers to deal with nonlinear
calibration curves, there's an awful lot of TCs and Thermistors in
use. The big advantage of the AD590 and PRT is that they are basically
linear over a convenient temperature range.

In a variety applications, other aspects of the measurement device are
important - ESD sensitivity, tolerance to wildly out of spec
temperature without damage, radiation effects etc.  Not an issue here,
but I'll note that the thermistor, PRT, and thermocouple are
essentially ESD immune. The AD590 most certainly is not.

If you go out and buy cheap industrial PID temperature controller it
will have input modes for various thermocouples and PRTs.  I suppose
there's probably some that take 1uA/K, but it's not something I would
expect.

So I wouldn't say thermistor bridges (or other temperature
measurements) are obsolete.

Hi

Ok, when you wrote the specification for your crystals what was the tolerance on the angle
for those crystals? What did the suppliers who quoted to your spec say about the angle tolerance
you specified? When they shipped against your volume requirements how did they do against the
specification? When your incoming QA tested the crystals what did they find? When you put the
crystals into production oscillators and tested the result how did they perform?

Bob

Hi

I think you have thermistors and thermocouples a bit mixed up. You can get
quite substantial output voltages from a thermistor bridge….

Bob